package cn.featherfly.servlet.http;

import java.util.Enumeration;

import cn.featherfly.servlet.ServletContext;

/**
 * Provides a way to identify a user across more than one page
 * request or visit to a Web site and to store information about that user.
 * <p>
 * The servlet container uses this interface to create a session
 * between an HTTP client and an HTTP server. The session persists
 * for a specified time period, across more than one connection or
 * page request from the user. A session usually corresponds to one
 * user, who may visit a site many times. The server can maintain a
 * session in many ways such as using cookies or rewriting URLs.
 * <p>
 * This interface allows servlets to
 * <ul>
 * <li>View and manipulate information about a session, such as
 * the session identifier, creation time, and last accessed time
 * <li>Bind objects to sessions, allowing user information to persist
 * across multiple user connections
 * </ul>
 * <p>
 * When an application stores an object in or removes an object from a
 * session, the session checks whether the object implements
 * {@link HttpSessionBindingListener}. If it does,
 * the servlet notifies the object that it has been bound to or unbound
 * from the session. Notifications are sent after the binding methods complete.
 * For session that are invalidated or expire, notifications are sent after
 * the session has been invalidated or expired.
 * <p>
 * When container migrates a session between VMs in a distributed container
 * setting, all session attributes implementing the {@link HttpSessionActivationListener}
 * interface are notified.
 * <p>
 * A servlet should be able to handle cases in which
 * the client does not choose to join a session, such as when cookies are
 * intentionally turned off. Until the client joins the session,
 * <code>isNew</code> returns <code>true</code>. If the client chooses
 * not to join
 * the session, <code>getSession</code> will return a different session
 * on each request, and <code>isNew</code> will always return
 * <code>true</code>.
 * <p>
 * Session information is scoped only to the current web application
 * (<code>ServletContext</code>), so information stored in one context
 * will not be directly visible in another.
 *
 * @author Various
 * @see HttpSessionBindingListener
 * @see HttpSessionContext
 */

public interface HttpSession {

    /**
     * Returns the time when this session was created, measured
     * in milliseconds since midnight January 1, 1970 GMT.
     *
     * @return a <code>long</code> specifying
     *         when this session was created,
     *         expressed in
     *         milliseconds since 1/1/1970 GMT
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    long getCreationTime();

    /**
     * Returns a string containing the unique identifier assigned
     * to this session. The identifier is assigned
     * by the servlet container and is implementation dependent.
     *
     * @return a string specifying the identifier
     *         assigned to this session
     */
    String getId();

    /**
     * Returns the last time the client sent a request associated with
     * this session, as the number of milliseconds since midnight
     * January 1, 1970 GMT, and marked by the time the container received the
     * request.
     * <p>
     * Actions that your application takes, such as getting or setting
     * a value associated with the session, do not affect the access
     * time.
     *
     * @return a <code>long</code>
     *         representing the last time
     *         the client sent a request associated
     *         with this session, expressed in
     *         milliseconds since 1/1/1970 GMT
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    long getLastAccessedTime();

    /**
     * Returns the ServletContext to which this session belongs.
     *
     * @return The ServletContext object for the web application
     * @since Servlet 2.3
     */
    ServletContext getServletContext();

    /**
     * Specifies the time, in seconds, between client requests before the
     * servlet container will invalidate this session.
     * <p>
     * An <tt>interval</tt> value of zero or less indicates that the
     * session should never timeout.
     *
     * @param interval An integer specifying the number
     *        of seconds
     */
    void setMaxInactiveInterval(int interval);

    /**
     * Returns the maximum time interval, in seconds, that
     * the servlet container will keep this session open between
     * client accesses. After this interval, the servlet container
     * will invalidate the session. The maximum time interval can be set
     * with the <code>setMaxInactiveInterval</code> method.
     * <p>
     * A return value of zero or less indicates that the
     * session will never timeout.
     *
     * @return an integer specifying the number of
     *         seconds this session remains open
     *         between client requests
     * @see #setMaxInactiveInterval
     */
    int getMaxInactiveInterval();

    /**
     * Returns the object bound with the specified name in this session, or
     * <code>null</code> if no object is bound under the name.
     *
     * @param name a string specifying the name of the object
     * @return the object with the specified name
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    Object getAttribute(String name);

    /**
     * Returns an <code>Enumeration</code> of <code>String</code> objects
     * containing the names of all the objects bound to this session.
     *
     * @return an <code>Enumeration</code> of
     *         <code>String</code> objects specifying the
     *         names of all the objects bound to
     *         this session
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    Enumeration<String> getAttributeNames();

    /**
     * Binds an object to this session, using the name specified.
     * If an object of the same name is already bound to the session,
     * the object is replaced.
     * <p>
     * After this method executes, and if the new object
     * implements <code>HttpSessionBindingListener</code>,
     * the container calls
     * <code>HttpSessionBindingListener.valueBound</code>. The container then
     * notifies any <code>HttpSessionAttributeListener</code>s in the web
     * application.
     * <p>
     * If an object was already bound to this session of this name
     * that implements <code>HttpSessionBindingListener</code>, its
     * <code>HttpSessionBindingListener.valueUnbound</code> method is called.
     * <p>
     * If the value passed in is null, this has the same effect as calling
     * <code>removeAttribute()</code>.
     *
     * @param name the name to which the object is bound;
     *        cannot be null
     * @param value the object to be bound
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    void setAttribute(String name, Object value);

    /**
     * Removes the object bound with the specified name from
     * this session. If the session does not have an object
     * bound with the specified name, this method does nothing.
     * <p>
     * After this method executes, and if the object
     * implements <code>HttpSessionBindingListener</code>,
     * the container calls
     * <code>HttpSessionBindingListener.valueUnbound</code>. The container
     * then notifies any <code>HttpSessionAttributeListener</code>s in the web
     * application.
     *
     * @param name the name of the object to
     *        remove from this session
     * @exception IllegalStateException if this method is called on an
     *            invalidated session
     */
    void removeAttribute(String name);

    /**
     * Invalidates this session then unbinds any objects bound
     * to it.
     *
     * @exception IllegalStateException if this method is called on an
     *            already invalidated session
     */
    void invalidate();

    /**
     * Returns <code>true</code> if the client does not yet know about the
     * session or if the client chooses not to join the session. For
     * example, if the server used only cookie-based sessions, and
     * the client had disabled the use of cookies, then a session would
     * be new on each request.
     *
     * @return <code>true</code> if the
     *         server has created a session,
     *         but the client has not yet joined
     * @exception IllegalStateException if this method is called on an
     *            already invalidated session
     */
    boolean isNew();

}
